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DOE-STD-1024-92
4.0
APPROACH SELECTED
As part of determining which approach was best to select, DOE
requested that Dr. C. A. Cornell assist in reviewing the existing LLNL and
EPRI results at the 69 commercial nuclear power plant sites (NPP).
Information in the form of hazard curves and hazard curve ratios (ratio of
the 85th percentile to the median, for peak ground acceleration and
several response spectral ordinates) was provided to Dr. Cornell and
DOE by Risk Engineering Inc. under contract to Martin Marietta Energy
Systems, Oak Ridge. This information was reviewed to determine if
there were any consistent trends in the uncertainty estimates within the
individual LLNL and EPRI studies, and to determine what the trends
were between the two studies. Figures 2 and 3 display typical
information provided. These figures show the ratio of 85th percentile to
the median for 10 hertz spectral frequency for the LLNL and EPRI
studies respectively.
Appendix C provides the full set of information on the hazard curve ratios
for the peak ground acceleration and the spectral frequencies of 25, 10,
5, 2.5 and 1 hertz. Several levels of ground motion are also shown on
each figure. Figures C1 to C6 display the geometric mean of the ratio
between the 85th percentile and the median for the EPRI results and the
LLNL results with and without LLNL-AE5. Figures C7 through C24
display the entire set of reactor data and the geometric mean, 15th and
85th percentiles of the data. As discussed below, the above data can be
used to derive a pseudo-mean correction factor for the seismic hazard
curves. Dr. Cornell's report is provided as Appendix D. The more
important trends observed are:
The site-to-site variability in the ratio of 85th/median in both the
LLNL and EPRI studies are very similar, for all ground motion cases
reviewed. This result is displayed on Figure 4 which shows the
ratio for a peak ground acceleration of 0.20g for the NPP sites. The
LLNL data shown on Figure 4 includes LLNL-AE5. The range of
the above ratio within either the LLNL or EPRI studies is about a
factor of 2 to 2.5 for the majority of the NPP sites;
The difference in the ratio of the 85th/median between the LLNL
and EPRI studies is very similar in a wide variety of cases. For
peak ground acceleration the difference between LLNL and EPRI is
represented by about a factor of 3 to 3.5 with LLNL-AE5 included,
falling to about a factor of 2 if LLNL-AE5 is not included. This trend
holds true for spectral velocities down to about 2.5 hertz. This trend
is displayed on Figure 5 which shows the geometric mean of the
ratio of the 85th percentile to the median for peak ground
acceleration;
14


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